Re: [PATCH V3 4/5] arm64: mm: introduce 52-bit userspace support

[Steve Capper <Steve.Capper@arm.com>]

On Fri, Nov 30, 2018 at 05:59:59PM +0000, Catalin Marinas wrote:
> On Wed, Nov 14, 2018 at 01:39:19PM +0000, Steve Capper wrote:
> > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> > index 50b1ef8584c0..19736520b724 100644
> > --- a/arch/arm64/include/asm/pgtable.h
> > +++ b/arch/arm64/include/asm/pgtable.h
> > @@ -616,11 +616,21 @@ static inline phys_addr_t pgd_page_paddr(pgd_t pgd)
> >  #define pgd_ERROR(pgd)		__pgd_error(__FILE__, __LINE__, pgd_val(pgd))
> >  
> >  /* to find an entry in a page-table-directory */
> > -#define pgd_index(addr)		(((addr) >> PGDIR_SHIFT) & (PTRS_PER_PGD - 1))
> > +#define pgd_index(addr, ptrs)		(((addr) >> PGDIR_SHIFT) & ((ptrs) - 1))
> > +#define _pgd_offset_raw(pgd, addr, ptrs) ((pgd) + pgd_index(addr, ptrs))
> > +#define pgd_offset_raw(pgd, addr)	(_pgd_offset_raw(pgd, addr, PTRS_PER_PGD))
> >  
> > -#define pgd_offset_raw(pgd, addr)	((pgd) + pgd_index(addr))
> > +static inline pgd_t *pgd_offset(const struct mm_struct *mm, unsigned long addr)
> > +{
> > +	pgd_t *ret;
> > +
> > +	if (IS_ENABLED(CONFIG_ARM64_52BIT_VA) && (mm != &init_mm))
> > +		ret = _pgd_offset_raw(mm->pgd, addr, 1ULL << (vabits_user - PGDIR_SHIFT));
> 
> I think we can make this a constant since the additional 4 bits of the
> user address should be 0 on a 48-bit VA. Once we get the 52-bit kernel
> VA supported, we can probably revert back to a single macro.

Yeah, I see what you mean.

> 
> Another option is to change  PTRS_PER_PGD etc. to cover the whole
> 52-bit, including the swapper_pg_dir, but with offsetting the TTBR1_EL1
> setting to keep the 48-bit kernel VA (for the time being).
> 

I've got a 52-bit PTRS_PER_PGD working now. I will clean things up, run
more tests and then post.

Cheers,
-- 
Steve